I-]-] THE FROG. 145 



a. Epithelial cells; columnar and elongated, each 

 with an oval nucleus, an unbranched peripheral 

 process and a branched basal one. 



b. Sensiferous cells ; more slender and often some- 

 what shorter than a. : generally to be recognized 

 by their swollen bases (enlarged around an en- 

 closed nucleus). Each terminates at its free end 

 in a cluster of delicate, hair-like, stiff processes, 

 and receives at its base a thread-like nerve-fibre. 



14. The auditory epithelium. 



Place sufficient of the membranous labyrinth to 

 embrace one of the ampullas (Sect. L. 4. c. y) in 1. 

 p. c. osmic acid solution for 3 — 4 hours ; transfer to 

 weak glycerine and tease up its epithelium with* a 

 couple of fine needles. Examine under your highest 

 power, and look for — 



a. Hair cells (sensiferous cells of auditory epithelium). 

 Each is pear-shaped and composed of a granular 

 protoplasm with a large round or oval nucleus : 

 from its flattened free end there stands out the 

 auditory hair ; a long pointed structure (from 3 

 to 4 times the length of the cell-body) seen, on 

 careful examination, to consist of several delicate 

 fibrils bound together. 



15. The skin. 



i. Cut out a piece of skin from the back of the thigh 

 of a recently killed frog : spread it out in water, 

 cover, and examine with a low power : note — 



a. The pigment-cells; black irregular patches; 

 some compact, others more or less branched. 



M. 10 



